1. Field of the Invention
The present invention relates to a rectifier for an automobile AC generator mounted on an engine of an automobile.
2. Description of the Related Art
FIG. 6 schematically shows a structure of an automobile AC generator 100.
In FIG. 6, a stator 1 is constructed of a stator core 2 and a stator coil 3 wound on this stator core 2. A rotor 4 is constituted by one pair of pole cores 5 and 6 located opposite to each other; an excitation coil 7 wound between the cores 5 and 6; a rotation shaft 8; and a slip ring 9 fixed on this rotation shaft 8. Then, a rear bracket 13 is fixed to a front bracket 12 by a fastening bolt 14, so that the stator 1 is supported between the front bracket 12 and the rear bracket 13. The rotation shaft 8 is supported via bearings 15 and 16 by the front bracket 12 and the rear bracket 13.
A pulley 17 is fixed to one end of the rotation shaft 8. A rectifier 18 is mounted on the rear bracket 13, and is electrically connected to an output terminal of the stator coil 3 so as to convert AC power generated by the stator 1 into DC power. A voltage regulator 19 is mounted to the rear bracket 13 in connection with a brush holder 20. The brush holder 20 supports a brush 21 in such a manner that this brush 21 abuts against the slip ring 9.
In the automobile AC generator 100 constituted in the above-described manner, a current is supplied via the brush 21 and the slip ring 9 to the excitation coil 7, and at the same time, rotation torque of an engine is transmitted via the pulley 17 and a belt (not shown) to the rotation shaft 8, so that the rotor 4 is rotary-driven. As a result, the stator 1 may generate AC power. Then, this AC power is converted into DC power by the rectifier 18.
Referring now to FIG. 7 to FIG. 10, the structure of this rectifier 18 will be described.
The rectifier 18 is arranged by a positive heat sink 30 on which a plurality of positive diodes 33 are mounted, a negative heat sink 31 on which a plurality of negative diodes 34 are mounted, and a circuit board assembly 32.
The positive heat sink 30 is made of aluminium. This positive heat sink 30 contains a arcuate body 30a, a plurality of heat radiating fins 30b, positioning guide portions 30c, and a plurality of positive diode mounting portions 30d. The plural heat radiating fins 30b stand upright on a rear surface of this arcuate body 30a. The positioning guide portions 30c are extended from three portions of this arcuate body 30a, namely both ends and a center of the arcuate body, outwardly along a radial direction. The plural positive diode mounting portions 30d are formed as concaves in a major surface of the arcuate body 30a along a circumferential direction thereof. Then, a plurality of positive diodes 33 are mounted on the major surface of the arcuate body 30a in such a manner that these positive diodes 33 are joined to the respective positive diodes mounting portions 30d.
The negative heat sink 31 is made of aluminum, and contains another arcuate body 31a, guide portions 31b, and a plurality of negative diode mounting portions 31c. The guide portions 31b are provided on three portions of this arcuate body 31a, namely both ends and a center portion thereof. The plural negative diode mounting portions 31c are formed as concaves on a major surface of the arcuate body 31a along a circumferential direction. Then, a plurality of negative diodes 34 are mounted on the major surface of the arcuate body 31a along the circumferential direction in such a manner that these diodes 34 are joined to the respective negative diode mounting portions 31c.
The circuit board assembly 32 is constructed of a resin member 36 formed in a arcuate shape and guide portions 36a formed on three portions of this resin member 36, i.e., both ends and a center portion thereof. This resin member 36 is made of an iron circuit board molded by polyphenylene sulfide resin (PPS). Then, connection terminals 37 of the circuit board assembly 32 are downwardly projected from the resin member 36 at a plurality of positions thereof along a circumferential direction.
The positive diode 33 is constituted in such a manner that an IC chip 33a is soldered on a copper base 33b to be joined, a relay lead 33c made of copper is soldered on the IC chip 33a to be joined, and further a lead 33d made of copper is soldered on the relay lead 33c to be joined, and these members are molded by resin. Then, the lead 33d is extended from a sealing resin member 33e, and is bent in an L-shape on the root side of the extended lead portion. Also, the negative diode 34 is formed in a similar manner to the above-explained positive diode 33.
In this case, the rectification performance of the rectifier 18, namely the performance of the diode may be substantially determined from the area of the IC chip. In general, this IC chip is formed as a square in view of the performance, the reliability, and the sealing characteristic and the productivity required when the peripheral portion of the IC chip is molded to constitute the diode. Such a square-shaped IC chip is overlapped with a frame for mounting a lead, and then is molded to manufacture a diode. A main body of this diode becomes a rectangular parallelepiped. A projection direction of the lead corresponds to a longitudinal direction. Also, this lead is projected at a right angle from one side among four sides, and a tip portion of this projected lead is bent perpendicular to the projection direction in order that this lead can be firmly connected to a frame functioning as a connection portion, and also sufficient strength can be achieved.
To assemble the rectifier 18 constituted in the above-described manner, while the lead 33d of the positive diode 33 is directed toward an outer circumference side, the copper base 33b is soldered/jointed to each of the positive diode mounting portions 30d of the positive heat sink 30. Similarly, while a lead 34d of the negative diode 34 is directed toward an inner circumference side, a copper base 34b is soldered/jointed to each of the negative diode mounting portions 31c of the negative heat sink 31. Then, the guide portions 30c of the positive heat sink 30 are overlapped via an insulating ring 35 to the guide portions 31b of the negative heat sink 31. Furthermore, the guide portions 36a of the circuit board assembly 32 are overlapped on the guide portion 30c of the positive heat sink 30. Thereafter, fastening bolts (not shown) are inserted under pressure into holes of the guide portions 30c, 31b, 36a, so that the positive heat sink 30, the negative heat sink 31, and the circuit board assembly 32 are positioned to be formed in an integral form.
At this time, the arcuate body 30a of the positive heat sink 30 is positioned on the inner circumferential side of the arcuate body 31a of the negative heat sink 31, and the major surfaces of both the arcuate bodies 30a and 31a are located at the same plane. Also, the lead 33d of the positive diode 33 is located opposite to the lead 34d of the negative diode 34, and the connection terminal 37 of the circuit board assembly 32 is interposed between the lead 33d and the lead 34d facing each other, respectively.
Then, the lead 33d of the positive diode 33, the lead 34d of the negative diode 34, and the connection terminal 37 of the circuit board assembly 32 are integrally joined with each other by means of the projection welding from both sides, so that the rectifier 18 is assembled.
The rectifier 18 assembled in the above-explained manner is mounted on a rear bracket 13 in a coaxial manner to a rotation shaft 8 in such a way that an inner circumferential edge surface of the arcuate body 30a of the positive heat sink 30 is positioned along a slip ring 9 of the rotation shaft 8.
As described above, since the rectifier of the automobile AC generator is arranged in such a coaxial manner to the rotation shaft 8 in order that the arcuate body 30a of the positive heat sink 30 may maintain a preselected clearance with respect to the slip ring 9 of the rotation shaft 8, the inner diameter of the arcuate body 30a of the positive heat sink 30 is determined by the outer diameter of the slip ring 9.
In other words, the inner diameter of the arcuate body 30a of the positive heat sink 30 becomes a fixed value. Then, in the conventional rectifier 18, the arcuate body 30a of the positive heat sink 30 is coaxially arranged with the arcuate body 31a of the negative heat sink 31 and further arrayed along the radial direction. In addition, the lead 33d of the positive diode 33 is so arranged as to abut against the lead 34d of the negative diode 34.
Therefore, the dimension of the conventional rectifier 18 along the radial direction requires at least a sum between the length of the positive diode 33 and the length of the negative diode 34. As a result, there is a problem that the conventional rectifier 18 cannot be made compact while maintaining the required performance.
Also, to realize compactness of the conventional rectifier 18, when the bending position of the lead 33d (34d) which is extended from the sealing resin member 33e (34e) and thereafter is bent in the L-shape is located close to the sealing resin member 33e (34e), the excessive stress is applied to the IC chip 33a (34a) while the lead 33d (34d) is bending-processed. In addition, the vibrations produced by the automobile are transferred to the lead 33d (34d), and therefore force is concentrated at the root portion of the lead 33d (34d). As a consequence, there is another problem that breakage failures readily occur in the leads and the IC chip, and thus the reliability is deteriorated.
On the other hand, under such a condition that the connection terminal 37 of the circuit board assembly 32 is sandwiched between the lead 33d of the positive diode 33 and the lead 34d of the negative diode 34, these connection terminal 37, lead 33d, and 34d are welded from both side by means of the projection welding. As a result, the heat generated at the boundary surfaces between the leads 33d, 34d and the connection terminals 37 when the different sorts of metals are joined with each other by means of the projection welding is diffused into the connection terminal 37, so that the heat is reserved into the center portion of the connection terminal 37 to thereby increase the temperatures of the connection terminal 37. Accordingly, a cavity is produced in the center portion of the connection terminal 37, so that the reliability is deteriorated. Under such a circumstance, the following alternative idea may be conceived. That is, in order to avoid that the cavity is produced in the center portion of the connection terminal 37, the thickness of the connection terminal 37 is made thicker. However, this alternative idea may cause the dimension of the conventional rectifier along the radial direction to be increased. Therefore, the down-sizing of a compact rectifier cannot be achieved.